1. Field of the Invention
This invention relates to an elevator which has a rising and falling cage connected by a cable of a traction machine. In particular, this invention relates to an elevator having control mechanisms for controlling the vibration of the cage.
2. Background
As shown in FIGS. 24 through 26, each of parallel guide rails 3 is disposed vertically on a rising and falling path 2. The vertical path 2 forms an elevator shaft in a building 1, and is further defined by a plurality of brackets 4 which typically represent the respective floors of building 1. Cage 5 rises and falls by a main cable 6 which is connected to a traction machine (not shown). Cage 5 is disposed within guide rails 3. As shown in FIG. 24, cage 5 consists of cage frame 5a and cage room 5b, and vibration-damping materials 7a, 7b are disposed between cage frame 5a and cage room 5b.
As shown in FIG. 25, supporting units 8 are disposed at each of the upper and lower corners of cage frame 5a, and approximately T-shaped operating levers 9 are pivoted to the supporting units 8 by pin-axles 9a. Guide rollers 10 are disposed to touch guide rails 3 and are connected to supporting unit 8 in the middle section of operating levers 9 through supporting axles 11.
Oil damper units 12, such as hydraulic cylinder units, are connected to one end portion of operating lever 9 by pin-axle 13 and are disposed on the cage 5. Guide levers 14, 15 pass through the upper section 9b of operating lever 9 and guide levers 14, 15 are disposed in an upper section of the supporting unit 8, and are parallel to each other. Nut Na prevents an adjusting spring 16 from coming off the end of guide lever 14. Guide roller 10 is pressed toward the guide rail 3 by adjusting spring 16. Nut Nb prevents a stopper 17 from coming off the end of guide lever 15, and stopper 17 restricts the range of movement of operating lever 9.
Guide rails 3 are originally constructed of steel or other metals or alloys thereof, and form a planar surface with guide roller 10. However, over prolonged use, guide rails 3 become worn particularly in the areas between respective floors. Thus, guide rails 3 form undulations in the form of windings as shown in FIG. 26.
When guide rails 3 have windings as shown in FIG. 26, operating levers 9 are displaced in response to buffers of the oil damper unit 12 and the adjusting spring 16. Vibration of cage 5, which occurs in response to the windings of the guide rails 3, is controlled due to the degree of displacement of the operating levers 9 permitted by damper unit 12 and adjusting spring 16.
When the distribution of load in cage 5 is inclined, namely, when cage 5 tilts, operating lever 9 touches the stopper 17 and cage 5 is prevented from tilting more than a predetermined value. Generally, the load in cage 5 is distributed evenly, and cage 5 is maintained in the level state. When the vibrations caused by the windings of the guide rails 3 are controlled by oil damper unit 12 and adjusting spring 16, external forces transmitted to cage 5 from guide rails 3 through guide rollers 10 are decreased. Accordingly, it is preferable that the spring constant of adjusting spring 16 and the coefficient of viscous damping of oil damper unit 12 are set at a lower level.
However, in the elevator as described above, when the spring constant of adjusting spring 16 is set at a lower level, operating lever 9 touches the stopper 17 at a comparatively small inclined load. Moreover, when cage 5 rises and falls at high speed, cage 5 is necessarily displaced by the windings of the guide rails 3. As a result, cage 5 rolls heavily.
As shown in FIG. 26, the wavelength of the winding of the guide rail 3 almost corresponds with each interval of the brackets 4. The interval of the brackets 4 is typically about 3 meters to about 5 meters, and the interval corresponds to the interval of floors in building 1. When cage 5 rises and falls along guide rails 3 at high speed, i.e., more than about 360 m/min, cage 5 is excited at about 2 to about 4 Hz of amplitude horizontally. When the excited frequency which occurs at the time that cage 5 passes through each of brackets 4 at high speed corresponds with the primary natural frequency of cage 5, (the primary natural frequency in the horizontal direction of cage 5 exists in the range of about 2 to about 4 Hz), the cage resonates. As a result, cage 5 rolls heavily.
It is effective to increase the coefficient of viscous damping of the oil damper unit 12 in order to reduce the amplitude of this resonance. However, this reduces the buffer of adjusting spring 16 against the excited force generated by the small windings of the guide rails 3. As a result, it becomes uncomfortable to ride in cage 5, and it is difficult to effectively prevent cage 5 from vibrating.